1. Field of the Invention
The present invention relates to a photoalignment material, a display substrate having an alignment layer formed using the same, and a method of manufacturing the display substrate. More particularly, the present invention relates to a photoalignment material used in a process for manufacturing an alignment layer of a liquid crystal display (LCD) apparatus, a display substrate having an alignment layer formed using the same, and a method of manufacturing the display substrate.
2. Background of the Invention
Generally, a liquid crystal display (LCD) panel includes a display substrate having a thin-film transistor (TFT) as a switching device to drive a pixel, an opposite substrate facing the display substrate, and a liquid crystal layer disposed between the display substrate and the opposite substrate. An image is displayed on the LCD panel according to the light transmittance of liquid crystal material, which changes according to voltage.
An alignment layer is formed on interior portions of each of the display substrate and the opposite substrate because it may be difficult to obtain an ideal liquid crystal molecular arrangement by simply disposing the liquid crystal material between the display substrate and the opposite substrate. The alignment layer may be formed by spreading a raw alignment material using a printing roller of an alignment layer printing apparatus on a base substrate and a rubbing process. For example, the raw alignment material may be a solution including a polyimide polymer.
Static electricity may be generated by rubbing with a rubbing cloth during the rubbing process in order to form the alignment layer, and thus the display substrate may be damaged by the static electricity. Moreover, the display substrate may be easily polluted and stained in the rubbing process, so that display quality may decrease. In order to prevent static electricity and improve display quality, a photoalignment process has been developed, wherein the process may include spreading a photoalignment material on the base substrate and photodegrading, photoisomerizing, or photopolymerizing the photoalignment material using light.
An example of the photoalignment material may include a diazo compound, which may be photoisomerized. However, the diazo compound may have low photosensitivity and low alignment stability, and may be decolored to become transparent.
Nowadays, a photoalignment material having a cinnamate, chalcone, or coumarin structure may be used in the photoalignment process using photoisomerization when forming an alignment layer, in order to improve the viewing angle. However, when a chemical compound having this structure is used, a radical reaction or a substitution reaction may be generated in addition to the photoisomerization reaction when light is irradiated because the molecules of the photoalignment material have many pi bonds. In this case, controlling the photoisomerization reaction may be difficult, and thus the reliability of the alignment layer may be decreased.